Field of the Invention
The present invention relates to a production process for a device which includes a structure formed by bonding two substrates and which has an opening such as an electric wire lead-out portion.
Description of the Related Art
In recent years, mass production of MEMS such as pressure sensors and acceleration sensors and of functional devices such as microfluidic devices is made possible by arranging multiple structures on a substrate by using a semiconductor process and forming chips of such devices. The aforementioned structures are fabricated in many cases by using a method of bonding two substrates on at least one of which detection elements are arranged. In this case, an electrode PAD for connecting each of the detection elements to an external device needs to be exposed. As a method of exposing the electrode PAD, there are disclosed a method of bonding upper and lower substrates in an offset manner (Japanese Patent Application Laid-Open No. H10-197907) and a method of bonding an electrode substrate and a substrate to be a cover which has an opening (Japanese Patent Application Laid-Open No. 2007-248281).
Problems in the conventional techniques are described by using FIGS. 1A1 to 1C2. These drawings show that a substrate illustrated in FIGS. 1A1 and 1A2 and a substrate illustrated in FIGS. 1B1 and 1B2 are bonded to each other and structures are thereby obtained in a bonded substrate illustrated in FIGS. 1C1 and 1C2. Note that FIGS. 1A1, 1B1, and 1C1 are plan views illustrating steps of fabricating multiple structures on one substrate, and FIGS. 1A2, 1B2, and 1C2 are cross-sectional views illustrating steps of fabricating one of the structures (the same applies to FIGS. 3A1 to 3E2 described later). When such structures are MEMS or microfluidic devices which have electric wiring, an electrode PAD 14 is required to establish electrical connection between the electric wiring and an external device such as a power supply. When the electrode PAD 14 is arranged on a bonding surface of an electrode substrate 11 which is to be bonded to a substrate 12 to be a cover (FIGS. 1A1 and 1A2), an opening 15 needs to be formed in the substrate to be the cover to enable connection with the electrode PAD 14 (FIGS. 1B1 and 1B2). If the opening 15 is formed in a substrate end portion, the rigidity of the substrate 12 decreases and this may lead to substrate breakage in conveying and transporting the substrate. Accordingly, an area without any opening needs to be provided in the substrate end portion to maintain the rigidity, i.e. no functional device can be arranged in the substrate end portion. Accordingly, the conventional techniques have a problem that the number of chips which can be obtained from one substrate is limited and utilization efficiency of the substrate cannot be improved.